An electrical engineer is telling his
lawyer friend about his latest home electronics project. The engineer
lives near some high-voltage power lines and is working on a device that
will harness the power of the 60Hz electromagnetic field that permeates
his property. The lawyer immediately states that what the engineer plans
to do would, in effect, be stealing from the utility company. This statement
angers the engineer who replies, “That’s the trouble with you
lawyers. You defend laws without regard to the truth. Even without
my device, the stray electromagnetic energy from the power lines is
radiated away and lost, so I might as well use it.” The lawyer stands
his ground and says the engineer will still be stealing.
Who is right? The lawyer is correct even though he probably doesn’t
know the difference between reactive and radiating electromagnetic
fields. The field surrounding the power lines is a reactive field, meaning
that it stores energy as opposed to radiating energy, so the engineer’s
device would in fact be “stealing” energy from the power lines. But why?
Why do some circuits produce fields that only store energy, while others
produce fields that radiate energy?
thought the power transmission line near his house was radiating energy
like an antenna, and that he was just collecting the radiating energy with
a receiving antenna. However, when the engineer measured the field on
his property, he was measuring the reactive field surrounding the power
transmission lines. When he activates his invention, he is coupling to the
reactive field and removing energy stored in the field surrounding the
power lines. The circuit he forms is analogous to the transformer circuit
in Figure 5.1B, so the engineer is, in fact, stealing the power.